diff --git a/hardware/arduino/cores/arduino/HardwareSerial.cpp b/hardware/arduino/cores/arduino/HardwareSerial.cpp
index 2e64acb82..719f3f6e3 100644
--- a/hardware/arduino/cores/arduino/HardwareSerial.cpp
+++ b/hardware/arduino/cores/arduino/HardwareSerial.cpp
@@ -34,6 +34,22 @@
 
 #include "HardwareSerial.h"
 
+/*
+ * on ATmega8, the uart and its bits are not numbered, so there is no "TXC0"
+ * definition.  It is slightly cleaner to define this here instead of having
+ * conditional code in the cpp module.
+ */
+#if !defined(TXC0)
+#if defined(TXC)
+#define TXC0 TXC
+#elif defined(TXC1)
+// Some devices have uart1 but no uart0
+#define TXC0 TXC1
+#else
+#error TXC0 not definable in HardwareSerial.h
+#endif
+#endif
+
 // Define constants and variables for buffering incoming serial data.  We're
 // using a ring buffer (I think), in which head is the index of the location
 // to which to write the next incoming character and tail is the index of the
diff --git a/hardware/arduino/cores/arduino/HardwareSerial.h b/hardware/arduino/cores/arduino/HardwareSerial.h
index 2b1de91cb..a73117f56 100644
--- a/hardware/arduino/cores/arduino/HardwareSerial.h
+++ b/hardware/arduino/cores/arduino/HardwareSerial.h
@@ -110,22 +110,6 @@ class HardwareSerial : public Stream
   extern HardwareSerial Serial3;
 #endif
 
-/*
- * on ATmega8, the uart and its bits are not numbered, so there is no "TXC0"
- * definition.  It is slightly cleaner to define this here instead of having
- * conditional code in the cpp module.
- */
-#if !defined(TXC0)
-#if defined(TXC)
-#define TXC0 TXC
-#elif defined(TXC1)
-// Some devices have uart1 but no uart0
-#define TXC0 TXC1
-#else
-#error TXC0 not definable in HardwareSerial.h
-#endif
-#endif
-
 extern void serialEventRun(void) __attribute__((weak));
 
 #endif